Mobile devices divided into several parts that are used in various combinations are being developed. Multipart radio terminals, for example, may include a cellular core unit and a number of optimized peripheral units. The peripheral units of the multipart radio terminals are optimized for specific tasks and all the peripheral units are connected to a core unit by low-power radio frequency (LPRF) connections, such as Bluetooth connections. One of the peripheral units may be optimized for making basic phone calls and another peripheral unit may be optimized for messaging and browsing or for imaging and music, for example. Typical mobile phones may also comprise several enhancement devices, such as headsets, pens, and web pads that communicate with the mobile phone over wireless connections.
All the peripheral units of a multipart radio terminal or enhancement devices of a mobile phone, for example, have different kinds of power consumption characteristics, that is, standby times and operation times, for example. These affect their individual average usage times between battery charges. A problem is that the user of the device has to constantly charge some devices or peripheral units and actively observe the battery statuses of several devices so that the whole set of devices remains operational. This creates inconvenience to the user.
Even if all the devices of the arrangement had equally long average use times, the compound use time of the whole system would be significantly less than with a system including one device alone. This is due to multiple devices running out of battery at random times in relation to each other. This phenomenon is familiar from the concept of MTBF (Mean Time Between Failures) in electronic components: one component can last a certain amount of time but if you connect two of them in sequence, the compound reliability of the system drops.